Interpretive Summary: Johne's disease is a chronic, debilitating intestinal disorder in cattle characterized by diarrhea, reduced feed intake, weight loss, and death. Cattle usually become infected as young calves by ingesting feces containing the causative bacteria. However, symptoms of disease do not usually present themselves until the animals reach 3 to 5 years of age or even older. During this time the animal is infected and may be shedding the organism in its feces without showing any clinical signs of disease. In addition to reduced production by these animals through reduced milk production, they also present a potential infective threat to the rest of the herd. The only current diagnostic test which can detect disease in subclinical animals is fecal culture. Drawbacks to fecal culture include highly specialized growth medium for this organism and the long incubation time (8-16 weeks). A new method which measures immune response to this bacteria has been shown in this study to be a very useful and sensitive technique for the detection of this disease.

Technical Abstract:
Peripheral blood mononuclear cells were isolated from noninfected control cows and from cows with either subclinical or clinical paratuberculosis (Johne's disease). Cells were incubated for 6, 12, 24, and 48 hours in complete medium with the following mitogens: concanavalin A (ConA), phytohemagglutinin-P (PHAP), pokeweed mitogen (PWM), and E. coli lipopolysaccharide (LPS). In addition, cells were incubated for the same time periods with a Mycobacterium paratuberculosis sonicate (MpS) and live and heat-killed M. paratuberculosis at 10:1 bacteria to cell ratio. After incubation, cell-free supernatants were analyzed for gamma-interferon (G-IF levels of G-IFN than did cells from clinical animals after stimulation with T-cell mitogens, ConA, PHAP, and PWM. Levels of G-IFN produced by noninfected control animals generally followed the pattern of subclinical animals. After incubation with MpS, significantly greater quantities of G- -cells from clinical cows and noninfected controls. Stimulation of cells with heat-killed or live M. paratuberculosis evoked a similar response. This study indicates that G-IFN production by peripheral blood mononuclear cells in response to M. paratuberculosis antigen may be an important diagnostic tool for the detection of paratuberculosis in subclinical animals.